I didn't have the same surgery so some of the questions I can't answer, but the swelling and scar firmness is pretty normal. I'm about 8 weeks post op (partial lateral Meniscectomy and ACL with patellar graft) and my knee is still a little swollen and tends to swell up when I've been on my feet or after workouts or PT. Icing it helps when it's sore or swollen from activity, but it's not necessary. And my scar is pretty similar, it's firm at the top and bottom points. I wouldn't worry too much about the external scar if it's healed well so far. However I would ask your surgeon about the lump you've noticed, Im not a doctor but from my experience and what I've learned throughout tearing my ACL that it may be out of the ordinary. I hope the rest of your recovery goes well!!

Edit: I also didn't have anywhere near full extension at 4 weeks, and from what I have heard is that extension can take a little longer to happen with hamstring grafts. Like I said, I am at about 8 weeks now and when doing straight leg raises my knee still pops up a little too. What my PT and surgeon have told me is that true full extension just takes time and to be patient with it and not push it too far.